Added generic RenderbufferStorage.DepthComponent

Tao had it as `Gl.GL_DEPTH_COMPONENT` and we need it badly https://github.com/Mailaender/OpenRA/commit/1a47db0f7cecf39559592512bc730223799d178d#commitcomment-6235712 as hard-coding those to specific ones caused problems in the past https://github.com/OpenRA/OpenRA/issues/3753.